F...

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M...

N...

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T...

Tainted mode

This mode tells Perl to internally mark any user input as untrustworthy. This
doesn't turn out to be a problem as long as this data is used purely internally
for calculations, etc., because they cannot be abused in any way.
Things look entirely differently when this data is supposed to be used for
potentially risky operations like opening a file. Perl, though, still won't
complain as long as the provided data is merely written to a file, but as soon
as this data is to be used to determine the location
at which to store a file, Perl is going to refuse to comply. In this case
danger is imminent that files get overwritten this way that normally should
have stayed untouched. In its normal mode of operation Perl would simply
execute the action. However, in Tainted mode Perl is going to abort with an
exception when it is told to perform any unsafe action with unverified user
input.